It has been reported that Parkinson's disease can be treated by transplantation of dopamine releasing cells and sever pain of end stage cancer patients can be alleviated by transplanting morphine releasing cells. Immunological reactions are most likely to be the reason for failure when transplanting allogeneic and xenogeneic cells. To overcome this problem, cells are transplanted after they are enclosed into a semipermeable polymer membrane, which must be permeable to small molecules such as oxygen, nutrients and bioactive substances, but impermeable to lymphocytes and immunoglobulins and complement proteins. In addition, it is difficult to find space for a large volume of transplant in central nerve system. Therefore, cen trifugal microencapsulation of cell aggregates was examined to solve these problems. Spherical cell aggregates were suspended into the alginate solution. 0.4 ml of the suspension was over-layed on the top of three layers composed of a 2.5 ml layer of 7 wt% dextran, a 0.5 ml layer of BaCl2 solution and a 0.5 ml layer Of 13 wt% dextran from the top in a 12 ml glass test-tube of 14 mm inner diameter. The test-tube was centrifuged at 170 x g for 10 min to spin the aggregates to the bottom of the tube. This procedure can effectively enclose cell aggregates in microcapsules with a very thin wall without contamination of empty microcapsules. The test-tube method can't be applied to microencapsulation of a large number of cell aggregates. A special centrifuge was developed. It can easily be operate and effectively microencapsulate a large number of cell aggregates, but there is a problem to solve in collecting microencapsulated aggregates from the centrifuge.